setEnablePlaceholders

Pass false to disable null placeholders in PagedLists using this Config.

If not set, defaults to true.

A PagedList will present null placeholders for not-yet-loaded content if two
conditions are met:

1) Its DataSource can count all unloaded items (so that the number of nulls to
present is known).

2) placeholders are not disabled on the Config.

Call setEnablePlaceholders(false) to ensure the receiver of the PagedList
(often a PagedListAdapter) doesn't need to account for null items.

If placeholders are disabled, not-yet-loaded content will not be present in the list.
Paging will still occur, but as items are loaded or removed, they will be signaled
as inserts to the PagedList.Callback.
onChanged(int, int) will not be issued as part of loading,
though a PagedListAdapter may still receive change events as a result of
PagedList diffing.

setPageSize

Configuring your page size depends on how your data is being loaded and used. Smaller
page sizes improve memory usage, latency, and avoid GC churn. Larger pages generally
improve loading throughput, to a point
(avoid loading more than 2MB from SQLite at once, since it incurs extra cost).

If you're loading data for very large, social-media style cards that take up most of
a screen, and your database isn't a bottleneck, 10-20 may make sense. If you're
displaying dozens of items in a tiled grid, which can present items during a scroll
much more quickly, consider closer to 100.

setPrefetchDistance

Defines how far from the edge of loaded content an access must be to trigger further
loading.

Should be several times the number of visible items onscreen.

If not set, defaults to page size.

A value of 0 indicates that no list items will be loaded until they are specifically
requested. This is generally not recommended, so that users don't observe a
placeholder item (with placeholders) or end of list (without) while scrolling.